1. Field of the Invention
The present invention relates to an organic light emitting display device and a method of manufacturing the same, and more particularly, to an organic light emitting display device that has a difference in charge mobility between a thin film transistor of a drive unit and a thin film transistor of a pixel unit, and a method of manufacturing the same.
2. Discussion of Related Art
An organic light emitting display device is a next generation display device which may actively emit light. Compared to a liquid crystal display device (LCD), the organic light emitting display device has excellent characteristics in view of view angle, contrast, response speed, power consumption, and other related functional properties.
An organic light emitting display device generally includes an organic light emitting diode that has an anode electrode, an organic light emitting layer, and a cathode electrode. The organic light emitting display device may be divided into a passive matrix type where the organic light emitting diode is connected between scan lines and signal lines in a matrix type to constitute a pixel, and an active matrix type where the operations of each pixel are controlled by a thin film transistor (TFT) that functions as a switch.
In the thin film transistor used in the active matrix type of organic light emitting display device, an activation layer provides source and drain regions, and a channel region. The activation layer is generally formed of a semiconductor layer made of amorphous silicon, poly-silicon, low temperature poly-silicon (LTPS), or other similar material.
In general, the amorphous silicon has a low mobility, therefore, the amorphous silicon is difficult to be implemented in a driving circuit which operates at a high speed. Therefore, the activation layer is generally made of the poly-silicon or the low temperature poly-silicon that has a high charge mobility compared to the amorphous silicon. However, the poly-silicon has a disadvantage that threshold voltage is uneven due to the nature of polycrystalline, and the low temperature poly-silicon has a disadvantage that a laser annealing or other related process for crystallization may be required during the manufacture of the poly-silicon.
Research and study on the oxide semiconductor which may be used as an activation layer have been recently conducted in order to solve the above identified problems.
Japanese Laid-Open Patent Publication No. 2004-273614 discloses a thin film transistor which has zinc oxide (ZnO) or an oxide semiconductor having zinc oxide (ZnO) as a main ingredient, as an activation layer.
An amorphous InGaZnO (Indium-Gallium-Zinc oxide; hereinafter, referred to as IGZO) has charge mobility higher by ten times (about 10 cm2/V·sec) compared to the amorphous silicon, and has even property distribution, therefore, the amorphous IGZO is sufficient for being used as the activation layer of the thin film transistor of the pixel unit. The amorphous IGZO is however insufficient for being used as the activation layer of the thin film transistor of the drive unit where a high charge mobility (about 100 cm2/V·sec) at a level of the low temperature poly-silicon is required. Furthermore, since the size and the requirement of the resolution of a display device are increased, the amount of data transmitted and the processing speed should be increased, and the most part of a driving circuit should be formed on one substrate in order to reduce the cost of manufacture. Therefore, significant problems may occur in stable property distribution and reliability of the thin film transistor of the drive unit.